Vehicles such as automobiles are provided with a transmission in order to properly take off driving force generated by an internal combustion engine while taking a running state of the vehicle into consideration. Among various transmissions, there are manually operated transmissions in which a driver manually converts and takes off driving force of an internal combustion engine in accordance with a required gear ratio and taking the running state of the vehicle into consideration, and automatic transmissions in which the driving force of an internal combustion engine is automatically converted and taken off in accordance with a required gear ratio and taking the vehicle running state into consideration.
Examples of such automatic transmissions are disclosed in Japanese Patent Early. Laid-open Publication Nos. Sho 63-1840 and Sho 62-196443.
A transmission disclosed in Japanese Patent Early Laid-open Publication No. Sho 63-1840 is of a type that driving force of an internal combustion engine is taken off through an electromagnetic clutch, a belt type non-stage transmission, and an auxiliary transmission having a forward gear, a reverse gear and a selector sleeve and which comprises a rotation control device for establishing a gear stage of the auxiliary transmission by rotating the selector sleeve relative to the forward gear or to the reverse gear, in the event the selector sleeve is not engaged with the forward gear or with the reverse gear when a shift mechanism is operated to a forwarding position or a reversing position.
A transmission disclosed in Japanese Patent Early Laid-open Publication No. Sho 62-196443 is of a type that driving force of an internal combustion engine is taken off through an automatic clutch, a stage transmission having a forward gear, a reverse gear and a selector sleeve, and a belt type non-stage transmission, and a predetermined amount of torque is transmitted for a short time through the automatic clutch, in the event the selector sleeve of the stage transmission is not engaged with the forward gear or with the reverse gear within a predetermined time after a shift mechanism is operated to a forwarding position or a reversing position.
One example of a shift control device of a transmission is shown in FIG. 14. In FIG. 14, the numeral 302 denotes a transmission. In this transmission 302, the gear ratio is, continuously and infinitesimally, varied by relatively increasing and decreasing the radius of rotation of a belt (not shown) looped around a primary sheave 304 and a secondary sheave 306 through oil pressure, and the driving force of an internal combustion engine is automatically converted and taken off in accordance with a required gear ratio and taking the running state of the vehicle into consideration.
This transmission 302 includes a hydraulic clutch 308 operated to be engaged and disengaged by oil pressure and a forward and reverse shifting mechanism 310 which can be shifted to a forward and reverse engagement state. The hydraulic clutch 308 is operated to be engaged and disengaged by oil pressure which is supplied to an oil pressure chamber not shown.
The forward and reverse shifting mechanism 310, as shown in FIG. 15, comprises a rotatable shaft 312, a forward shifting gear 316 forming a forward gear train 314, a reverse shifting gear 320 forming a reverse gear train 318, said gears 316 and 320 being rotatably supported on the rotatable shaft 312, and a selector sleeve 322 nonrotatably mounted on the rotatable shaft 312 and supported thereon for movement in the axial direction, the selector sleeve 322 selectively connecting either the forward shifting gear 316 or the reverse shifting gear 320 to the rotatable shaft 312 to attain a forward and reverse engagement state.
The transmission 302 is provided with an oil pump 324 for generating oil pressure for operating the primary sheave 304, secondary sheave 306, hydraulic clutch 308, and forward and reverse shifting mechanism 310. The oil pump 324 is connected at an intake side thereof with an oil pan (not shown) through a strainer 326 and connected at an outlet side thereof with a line pressure passage 328. The line pressure passage 328 is connected with a first line pressure control valve 330, a second line pressure control valve 332, a ratio control valve 334, a solenoid regulator valve 336, and a relief valve 338.
The solenoid regulator valve 336 is connected with the first line pressure control valve 330 and ratio control valve 334 through a line solenoid valve 340 and a resin solenoid valve 342, respectively. The second line pressure control valve 332 is connected with a lubrication system for lubricating a belt (not shown) and with an intake side of the oil pump through a loop regulator valve 344. This loop regulator valve 344 is connected with a cooling control valve 346. The cooling control valve 346 is connected with an oil cooler 348 and the hydraulic clutch 308.
Also, the line pressure passage 328 is connected with a clutch control valve 350 for regulating clutch pressure as oil pressure which is to be supplied to the hydraulic clutch 308. The clutch control valve 350 is connected with the solenoid regulator valve 336 through a clutch solenoid valve 352. The oil pressure regulated by the clutch control valve 350 is supplied to and exhausted from a manual shift valve 354 through a shift servo valve 356.
The manual shift valve 354 is connected with the line pressure passage 328. The manual shift valve 354 comprises a valve body 358, a manual shift rod 362 slidably disposed within a slide hole 360 of the valve body 358, and a spool valve element 364 integral with the manual shift rod 362.
The shift servo valve 356 comprises a valve body 366, a piston 370 slidably disposed within a cylinder 368 of the valve body 366, a first chamber 372 and a second chamber 374 being defined within the cylinder 364 by the piston 370, a shift side rod 376 connected to one end of the piston 370, a spool valve element 378 disposed at an intermediate portion of the shift side rod 376, and a shift fork 380 fixed to the rod 376 on a side of valve element 378 opposite piston 370. The shift fork 380 is engagable with the selector sleeve 322 of the forward and reverse shifting mechanism 310.
The manual shift valve 354 is shifted by an operating rod 384 (FIG. 15) of a shift mechanism 382, thereby supplying and exhausting oil pressure from the clutch control valve 350 and line pressure passage 328 to and from the shift servo valve 356. The shift servo valve 356 is shifted by supplying and exhausting oil pressure from the line pressure passage 328 through the manual shift valve 354 to and from the first and second chambers 372 and 374, thereby supplying and exhausting oil pressure to and from the hydraulic clutch 308 and shifting the forward and reverse shifting mechanism 310.
Therefore, in the shift servo valve 356, oil pressure is normally supplied either to the first chamber 372 or to the second chamber 374 and force for pushing the rod 376 either in direction A or in direction B is normally produced as shown in FIGS. 16 through 20.
The shift mechanism 382 has various operating positions such as, for example, a parking position P, a reversing position R, a neutral position N, a forwarding position D, and a low speed running position L. In the respective operating positions P, R, N, D and L of the shift mechanism 382, the manual shift valve 354 and the shift servo valve 356 are shifted as shown in FIGS. 16 through 20, respectively.
At this time, in the respective operating positions P, R, N, D and L of the shift mechanism 382, the forward and reverse shifting mechanism 310 is brought into the following engagement states such as, for example, a forward engagement state FWD and a reverse engagement state REV. That is, in the parking position P and in the reversing position R, force for pushing the shift servo rod 376 in the direction B is produced because oil pressure is supplied into the second chamber 374 of the shift servo valve 356, and shifting mechanism 310 is held in the reverse engagement state REV. In the neutral position N, forwarding position D and low-speed running position L, a force is produced for pushing the shift servo rod 376 in the direction A because oil pressure is supplied into the first chamber 372 of the shift servo valve 356, and shifting mechanism 310 is brought into the forward engagement state FWD. This operation is summarized as follows:
______________________________________ Operating Position Engagement State ______________________________________ P REV R REV N FWD D FWD L FWD ______________________________________
That is, shifting operation between the forward engagement state FWD and reverse engagement state REV of the forward and reverse shifting mechanism 310 is performed between the reversing position R and the neutral position N of the shift mechanism 382. Otherwise, shifting operation between the forward engagement state FWD and the reverse engagement state REV of the forward and reverse shifting mechanism 310 is sometimes performed between the neutral position N and the forwarding position D of the shift mechanism 382.
Accordingly, shifting operation between the forward engagement state FWD and the reverse engagement state REV of the forward and reverse shifting mechanism 310 is performed between one particular operating position of the shift mechanism 382 and another operating position adjacent to this one operating position.
However, in such conventional shift control devices, since shifting operation between the forward engagement state FWD and the reverse engagement state REV of the forward and reverse shifting mechanism 310 is performed between one particular operating position of the shift mechanism and another operating position adjacent to this one operation position as mentioned above, there is a problem in that, when shifting operation of the forward and reverse shifting mechanism 310 does not go well, operation of the shift mechanism 382 for overcoming this unfavorable condition of shifting operation is difficult to perform.
For example, in a shift control device of a transmission in which shifting operation between the forward engagement state FWD and the reverse engagement state REV of the forward and reverse shifting mechanism 310 is performed between the reversing position R and the neutral position N of the shift mechanism 382, when the shift mechanism 382 is operated from the reversing position R to the forwarding position D via the neutral position N, the forward and reverse shifting mechanism 310 is initially in the reverse engagement state REV (FIG. 17), and when the shift mechanism 382 is operated to the neutral position N, it is shifted to the forward engagement state FWD (FIG. 18).
At this time, when shifting operation of the forward and reverse shifting mechanism 310 does not go well, it becomes impossible for the vehicle to run even if the shift mechanism 382 is operated to the forwarding position D because driving force cannot be transmitted to the wheels.
In such instance, a driver usually tries to overcome the unfavorable condition of the forward and reverse shifting mechanism 310 by operating the shift mechanism 382 again to the forwarding position D after it is once operated to the neutral position N. However, since the engagement state of the forward and reverse shifting mechanism 310 is the forward engagement state FWD both in the neutral position N and forwarding position D, oil pressure to be supplied to and exhausted from the first and second chambers 372 and 374 of the shift servo valve 356 pushes the piston 370 in the direction A in order to bring the forward and reverse shifting mechanism 310 into the forward engagement state FWD. As a consequence, the unfavorable condition of shifting operation of the forward and reverse shifting mechanism 310 is impossible to overcome. In order to overcome the unfavorable condition of shifting operation, it is necessary to operate the shift mechanism 382 again to the forwarding position D via the neutral position N after it is once operated to the reversing position R.
However, there is an inconvenience in that the driver has a psychological resistance to operating the shift mechanism 382 again to the forwarding position D via the neutral position N after it is once operated to the reversing position R when shifting operation of the forward and reverse shifting mechanism 310 does not go well. Thus, the operation for overcoming the unfavorable condition of shifting operation is difficult to perform with ease.
That is, the driver usually considers that the shifting operation trouble is due to the operation for shifting the shift mechanism 382 from the neutral position N to the forwarding position D in the event shifting operation of the forward and reverse shifting mechanism 310 does not go well when the shift mechanism 382 is operated from the neutral position N to the forwarding position D, and therefore, the idea of operating the shift mechanism 382 to the reversing position R usually does not occur to the driver.
As a consequence, there is an inconvenience since the driver has a psychological resistance to operating the shift mechanism 382 once to the reversing position R, and the operation required for overcoming the unfavorable condition of shifting operation is difficult to perform with ease.
Furthermore, there is a significant problem in the conventional shift control device of a transmission in that, where the shift mechanism 382 is operated between the neutral position N and the reversing position R particularly in a low temperature state of oil pressure, a larger sound of shifting operation of the forward and reverse shifting mechanism 310 is generated at the time shifting operation is made from the reversing position R to the neutral position N than at the time the shifting operation is made from the neutral position N to the reversing position R.
When the shift mechanism 382 is operated from the reversing position R to the neutral position N, the manual shift valve 354 is shifted to supply line pressure as oil pressure to the first chamber 372 of the shift servo valve 356 to exhaust line pressure in the second chamber 374, thereby moving the piston 370 in the direction A in FIGS. 17 and 18. At this time, in the reversing position R, the hydraulic clutch 308 is, as shown in FIG. 17, supplied with clutch pressure as oil pressure from the manual shift valve 354 through the shift servo valve 356 and engaged. Similarly, in the reversing position R, the forward and reverse shifting mechanism 310 is in the reverse engagement state REV.
When the shift mechanism 382 is operated to the neutral position N, the hydraulic clutch 308 is disengaged because, as shown in FIG. 18, clutch pressure as oil pressure is exhausted from the clutch through the shift servo valve 356 and the manual shift valve 354.
Furthermore, in shifting from reverse R to the neutral position N, the forward and reverse shifting mechanism 310 is shifted from the reverse engagement state REV to the forward engagement state FWD. In this way, when the shift mechanism 382 is operated from the reversing position R to the neutral position N, clutch pressure as oil pressure is exhausted from the hydraulic clutch 308 and the forward and reverse shifting mechanism 310 is shifted from the reverse engagement state REV to the forward engagement state FWD.
However, since the shifting operation of the shift servo valve 356 is faster than the exhaust of clutch pressure from the hydraulic clutch 308 and the shifting operation of the shift servo valve 356 becomes faster than the exhaust of clutch pressure from the hydraulic clutch 308 because viscosity of oil pressure is increased particularly at a low oil temperature, shifting operation of the forward and reverse shifting mechanism 310 to the forward engagement state FWD is performed before clutch pressure is completely exhausted from the hydraulic clutch 308, that is, before the hydraulic clutch 308 is fully disengaged. This becomes a cause for generating a sound of shifting operation caused by engagement of the forwarding gear train 314.
Where the shift mechanism 382 is shifted from the neutral position N to the reversing position R, clutch pressure as oil pressure is already completely exhausted from the hydraulic clutch 308 in the neutral position N and when the shift mechanism 382 is operated to the reversing position R, clutch pressure as oil pressure is supplied to the hydraulic clutch 308 and the forward and reverse shifting mechanism 310 is shifted from the forward engagement state FWD to the reverse engagement state REV. At this time, the shifting operation of the forward and reverse shifting mechanism 310 from the forward engagement state FWD to the reverse engagement state REV is completed before clutch pressure is supplied to the hydraulic clutch 308, that is, the hydraulic clutch is not yet fully engaged because shifting operation of the shift servo valve 356 is faster than the supply of clutch pressure to the hydraulic clutch 308. Thus, a sound of shifting operation caused by engagement of the reverse gear train 318 is not generated.
It is therefore an object of the present invention to provide a shift control device of a transmission capable of providing an easy operation for overcoming trouble when the shifting operation of the forward and reverse shifting mechanism does not go well and also capable of reducing the generation of a sound of shifting operation of the forward and reverse shifting mechanism, especially when the temperature is low.
In attempting to achieve the above-mentioned object, the present invention is designed such that in a shift control device of a transmission comprising a manual shift valve shifted by a shift mechanism of a transmission having a hydraulic clutch operated to be connected and disconnected by oil pressure and a forward and reverse shifting mechanism shiftable to forward and reverse engagement states and adapted to supply and exhaust oil pressure, and a shift servo valve shifted by oil pressure supplied and exhausted by the manual shift valve. The shift control device is characterized in that it further comprises an oil pressure supply and exhaust mechanism operated to shift the shift servo valve by supplying and exhausting oil pressure to and from the shift servo valve, so that when the shift mechanism is operated from a reversing position to a forwarding position via a neutral position, the shift servo valve is operated to hold the forward and reverse shifting mechanism in the reverse engagement state until the shift mechanism is operated to the neutral position and to shift the forward and reverse shifting mechanism to the forward engagement state when the shift mechanism is operated to the forwarding position, and when the shift mechanism is operated from the forwarding position to the reversing position via the neutral position, the shift servo valve is operated to hold the forward and reverse shifting mechanism in the forward engagement state until the shift mechanism is operated to the neutral position and to shift the forward and reverse shifting mechanism to the reverse engagement state when the shift mechanism is operated to the reversing position.
According to the construction of the present invention, the oil pressure supply and exhaust mechanism is operated to shift the shift servo valve by supplying and exhausting oil pressure to and from the shift servo valve, so that when the shift mechanism is operated from a reversing position to a forwarding position via a neutral position, or when the shift mechanism is operated from a forwarding position to a reversing position via a neutral position, the forward and reverse shifting mechanism is held in a reverse engagement state in a reversing position or in a forward engagement state in a forwarding position which is one position before the shift mechanism is shifted to the neutral position, and when the shift mechanism is operated from the neutral position to the forwarding position or to the reversing position, the forward and reverse shifting mechanism is shifted to the forward engagement state or to the reverse engagement state.
By this, since pressure oil of the shift servo valve is once exhausted in the neutral position and pressure oil is newly supplied to the shift servo valve when the shift mechanism is operated again to the forwarding position or reversing position by operating the shift mechanism again to the forwarding position or to the reversing position after the shift mechanism is once operated to the neutral position when shifting operation of the forward and reverse shifting mechanism does not go well, a reliable shifting operation can be obtained.
Similarly, when the shift mechanism is operated from the neutral position to the forwarding position or to the reversing position, the forward and reverse shifting mechanism is shifted to the forward engagement state or to the reverse engagement state. As a consequence, shifting operation of the forward and reverse shifting mechanism can be performed in a state where the hydraulic clutch, disengaged in the neutral position, is engaged by means of operation of the shift mechanism to the forwarding position or to the reversing operation, in other words, in a state where the hydraulic clutch is not fully engaged.
Referring to Japanese Patent Early Laid-open Publication No. Sho 62-196443, a shift control method of a transmission for the use of a vehicle disclosed in this publication is designed such that when a sleeve of a synchromesh device is not brought to a position indicating establishment of a gear stage of a stage transmission within a predetermined time after a shift lever is operated from a non-running state to a running state, a predetermined amount of torque is transmitted in a short time through an automatic clutch to exert relative force of rotation between a synchronous ring of the synchromesh device and output gear of the stage transmission, thereby making it possible to effect relative rotation of the synchronous ring and output gear which were unable to effect relative rotation and overcoming unableness of shift of the gear stage caused by unfavorable relative rotation.
Referring to Japanese Patent Early Laid-open Publication No. Sho 63-1840, a transmission for the use of a vehicle equipped with a secondary transmission disclosed in this publication is designed such that in the event a sleeve is not brought to a first or second position notwithstanding that a shift operating lever is shifted to a forward or reverse range when a vehicle stops, rotation of a rotatable member is permitted by a predetermined amount in order to rotate a forward or reverse gear by a predetermined amount relative to the sleeve, so that interference between the sleeve and the forward or reverse gear is promptly removed, generation of gear meshing sound is restrained, and the gear stage of the secondary transmission is more reliably established.
Furthermore, regarding the shift mechanism of a non-stage transmission, almost all of Japanese Patent Early Laid-open Publication Nos Sho 57-144338, Sho 57-144339, Sho 58-156754, Sho 60-159452, and Sho 60-159453 employ a mechanical type shift mechanism. This mechanical type shift mechanism is widely used. However, if a hydraulic type shift mechanism is used, there can be obtained an advantage in that shift operation can be smoothly performed when compared with the mechanical type shift mechanism. Therefore, the hydraulic shift mechanism is being widely used in recent time.
Furthermore, as is shown in FIG. 34, clutch pressure and line pressure are respectively supplied to the manual shift valve 472 of a hydraulic control circuit 404 of a hydraulic type shift mechanism, and clutch pressure and line pressure are also respectively supplied to the shift servo valve 480.
In one type of conventional shift control device of a transmission, a forward and reverse shifting mechanism for shifting, for example, a forward and reverse engagement state of a transmission, is mechanically shifted by a shift mechanism. In the case of such mechanical type shift mechanism, a smooth shifting operation is unobtainable.
In view of the foregoing, there is another type in which a manual shift valve is shifted by a shift mechanism in order to supply and exhaust oil pressure to and from a shift servo valve. A forward and reverse shifting mechanism for shifting, for example, a forward and reverse engagement state of a transmission, is shifted by this shift servo valve. According to such hydraulic type shift mechanism, shifting operation can be smoothly performed.
However, in the hydraulic servo type shift mechanism, there sometimes occurs a stop phenomenon indicating unfavorable engagement, in which chamfer parts where a gear and a sleeve are meshed are abutted at generally tops thereof with respect to each other when shifting operation is performed.
A similar stop phenomenon also occurs in the mechanical type shift mechanism. However, in the mechanical type shift mechanism, since a select lever is directly connected in motion with a shift part, the select lever is not operated until it is brought to an indicated position when a stop phenomenon indicating an unfavorable engagement occurs. Therefore, since the unfavorable engagement state can be confirmed, the shifting operation is newly performed again by operating the select lever again.
However, the hydraulic type shift mechanism has an inconvenience in that the select lever is operated to an indicated position when a stop phenomenon caused by wrong shifting, i.e., unfavorable engagement, occurs, and driving force is not transmitted because of occurrence of the stop phenomenon notwithstanding that D range or R range is indicated, and as a result, a vehicle becomes unable to start running.
It can be considered that when a stop phenomenon occurs, either a gear or a sleeve is rotated to remove the stop phenomenon and to complete the shifting operation. However, if a clutch is connected in order to rotate a gear when a stop phenomenon occurs, a ratchet sound (for instance, scratching sound) is generated at the chamfer parts and at least either the gear or sleeve is damaged.
It is, therefore, another object of the present invention to provide a shift control device of a transmission able to overcome an unfavorable engagement between either a forward gear or reverse gear and a shift member and to perform a reliable shifting operation. The device includes a shift servo valve for making clutch pressure into servo cylinder pressure in order to shift a forward and reverse shifting mechanism for shifting a forward and reverse engagement state of the non-stage transmission so as to supply and exhaust oil pressure, and a confirmation switch disposed at one end portion of a shift servo rod of the shift servo valve and adapted to confirm the position of the shift servo valve. At least the servo cylinder pressure of the shift servo valve is lowered when an unfavorable engagement state between either the forward gear or reverse gear and the shift member of the forward and reverse shifting mechanism is confirmed by the confirmation switch, and then the servo cylinder pressure is raised again in order to overcome the unfavorable engagement state between either the forward gear or reverse gear and the shift member of the forward and reverse shifting mechanism.
To achieve the above object, the present invention is constituted such that in a transmission for taking off driving force of an internal combustion engine in accordance with a running state of a vehicle after it is converted into a required gear ratio and having a hydraulic clutch which is connected and disconnected by means of supply and exhaust of oil pressure in order to engage and disengage engine driving force, a shift control device of said transmission is characterized in that it includes a forward and reverse shifting mechanism for shifting a forward and reverse engagement state of said non-stage transmission by a forward gear, a reverse gear and a shift member between said forward and reverse gears, a shift servo valve for making clutch pressure into servo cylinder pressure in order to supply and exhaust oil pressure by shifting said forward and reverse shifting mechanism, and a confirmation switch disposed at one end portion of a shift servo rod of said shift servo valve and adapted to confirm the position of said shift servo valve. At least the servo cylinder pressure of said shift servo valve is lowered when an unfavorable engagement state between either said forward gear or reverse gear and said shift member of said forward and reverse shifting mechanism is confirmed by said confirmation switch, and then the servo cylinder pressure is raised again in order to overcome the unfavorable engagement state between either said forward gear or reverse gear and said shift member of said forward and reverse shifting mechanism.
By virtue of the foregoing construction, when engagement between either the forward gear or reverse gear and the shift member is unfavorable, the servo cylinder pressure is lowered and then the servo cylinder pressure is raised again to overcome the unfavorable engagement between either the forward gear or reverse gear and the shift member of the forward and reverse shifting mechanism, thereby ensuring a reliable shifting operation .